Process for forming a film

ABSTRACT

A process for forming a built-up film with high polymers whose film inherently cannot be readily obtained by LB technique comprises modifying the high polymers, and if required, further by cyclizing the product partially or wholly, the produced thin films have extremely excellent heat resistance, good chemical resistance and mechanical characteristics and whose thickness is so small that it is generally hardly attainable, that is, less than 10,000  ANGSTROM , or if desired, super-thin films of 10 to 1000  ANGSTROM .

This application is a continuation of application Ser. No. 267,593 filedNov. 7, 1988 now abandoned, which is a division, of application Ser. No.905,415 filed Sept. 10, 1986 now U.S. Pat. No. 4,801,420.

FIELD OF THE INVENTION

This invention relates to a process for forming a film of high polymer,and more particularly to a process for forming a film of a modified highpolymer by the Langmuir-Blodgett process.

BACKGROUND OF THE INVENTION

Already in 1930's it was found out by Langmuir and Blodgett that fattyacids having about 16 to 22 carbon atoms form a monomolecular film onthe surface of water and such a film can be built up on a substrate, butit is only within recent years that its technical application began tobe investigated.

The outline of the investigation hitherto made has been reviewed in"Kotai Butsuri" (Physics of Solids) 17 (12) 45 (1982), Thin Solid Film68 No. 1 (1980), ibid, 99 No. 1, 2, 3 (1983), Insoluble monolayers atliquid-gas interface (G. L. Gains, Interscience Publishers, New York,1966), etc., but the conventional Langmuir-Blodgett films (hereinafterreferred to as "LB film") of straight chain saturated carboxylic acidsare defective in the points of heat resistance and mechanical strength,and so there is a problem that they can find no practical application asthey are.

In order to improve these defects investigations were made onpolymerized films of unsaturated fatty acids such as ω-tricosenic acid,ω-heptadecenic acid, or α-octadecylacrylic acid; unsaturated esters offatty acids such as vinyl stearate, octadecyl acrylate; and besidesthese, diacetylene derivatives, etc., but they can be said to be neithersufficiently heat-resistant nor electrically excellent. As for polymers,it is known that some of the high polymers having hydrophilic groupssuch as polyacids, polyalcohols, ethyl acrylate, polypeptides, etc. arepossessed of a film-forming property, but any sort of modified highpolymer suitable for LB materials has not as yet been investigated, andthere are no excellent material for the LB film worthy of the name.

On the other hand, as a heat-resistant film there may be mentionedpolyimide, but the thickness of the film of this material obtainedaccording to the spin coating process is not less than 1000 Å, andusually not less than 1 micron, so that it is very difficult to produceheat-resistant thin film of a thickness not more than 1000 Å and freefrom pin holes.

SUMMARY OF THE INVENTION

The object of this invention is to make feasible the film formation by aLangmuir-Blodgett technique, by modifying the high polymers which areinherently difficult to be formed into film according to theLangmuir-Blodgett technique, and to provide high polymer films whichhave a thickness hitherto never obtained easily by the conventionalprocess along with improved heat resistance, chemical resistance, andmechanical characteristics such as adhesive strength, etc.

According to the present invention, there is provided a process forforming a built-up film by the Langmuir-Blodgett technique with a highpolymer which contains linear repeating units composed of the firstorganic group R₁ and the second organic group R₂, each being at leastdivalent and having at least two carbon atoms, and both being connectedwith each other by a divalent bonding group, and at least one of thehydrocarbon-containing groups R₃ and R₄ of 10 to 30 carbon atoms, whichmay have substituent groups, bonded to the repeating units by covalentbonding.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 indicates the infrared absorption spectrum of the high polymerobtained in Example 1, and

FIG. 2 indicates the result of the thermogravimetric analysis.

FIG. 3 indicates the weight changes (TGA) and the heat changes (DTA)when the temperature was elevated from room temperature to 400° C.,after holding this temperature for one hour, lowered to roomtemperature, and then elevated to 1000° C.

FIG. 4 indicates the relation between the surface pressure and the areaper repeating unit when the precursor obtained in Example 1 was spreadon the surface of water in accordance with Example 2. FIG. 5 indicatesthe result of the FT-IR of the product obtained by building up the aboveon a plate of CaF₂ by the Langmuir-Blodgett technique.

FIG. 6 indicates the surface pressure vs area curve of the precursorobtained in Example 3.

FIG. 7 is the infrared spectrum of the high polymer obtained in Example5, and

FIG. 8 is the result of the thermogravimetric analysis.

FIG. 9 indicates the relation between the surface pressure and the areaper repeating unit of the high polymer obtained in Example 5.

DETAILED DESCRIPTION OF THE INVENTION

In this invention high polymers are modified so that they can be formedinto film by the Langmuir-Blodgett technique by introducing thesubstituent groups for imparting hydrophobic property to the repeatingunits of said high polymers, and the thus modified high polymers areused for the film formation by the Langmuir-Blodgett technique.

The material of the LB film used in this invention is a high polymerwhich contains linear repeating units comprised of the first organicgroup R₁ and the second organic group R₂, each being at least divalentand having at least two carbon atoms, and both being connected with eachother by divalent bonding group, and at least one of thehydrocarbon-containing groups R₃ and R₄ of 10 to 30 carbon atoms, whichmay have substituent groups, bonded to the repeating units by covalentbonding.

To explain in more detail, the high polymers of this invention arecomposed of

    --A--R.sub.1 --AB--R.sub.2 --B--                           (1)

    --A--R.sub.1 --BA--R.sub.2 --B--                           (2)

    --B--R.sub.1 --BA--R.sub.2 --A--                           (3)

as the linear repeating units forming the basic skeleton.

Herein R₁ and R₂ are at least a divalent group having at least twocarbon atoms, preferably 5 to 20 carbon atoms. It may be an aromaticgroup; an alicyclic group; an aliphatic group; a group wherein anaromatic group and an aliphatic group are combined; a group wherein eachof the above-mentioned groups is substituted by a monovalent grouphaving 1 to 30 carbon atoms selected from the group consisting of analiphatic group, an alicyclic group, an aromatic group, and a group inwhich an aliphatic group is combined with an alicyclic group or anaromatic group; or a group wherein each of the preceding groups issubstituted by a monovalent group such as a halogen atom, nitro group,amino group, cyano group, methoxyl group or acetoxyl group, or by agroup in which the above monovalent group bonds to --O--, --COO--,--NHCO--, --CO--, --S--, --CSS--, --NHCS--, --CS--, or the like. Groupscharacterized by benzenoid unsaturation having at least 6 carbon atomsare preferred as R₁ and R₂ in points of heat resistance, chemicalresistance and mechanical properties.

AB and BA in formulae (1) to (3) represent a divalent bonding groupformed by the reaction of an acidic group A and a basic group Bcontaining a hetero-atom such as 0, N, S, P, B, etc. More particularly,they are the groups formed by the reaction of an acidic group such as--COOR (R is an alkyl group or a hydrogen atom The same shall applyhereinafter), --COX (X is Cl or Br. The same shall apply hereinafter),--NCO, --NCS, --CN, --CONHR, etc. and a basic group such as --NHR",--OR", --SR", --X, etc., and ##STR1##

The high polymers of this invention are those which were modified sothat they may be formed into films by the Langmuir-Blodgett technique byintroducing into the repeating units as the basic skeleton shown by (1)to (3), at least one of the hydrocarbon-containing groups R₃ and R₄ of10 to 30 carbon atoms, preferably 16 to 22, which may have substituentgroups, bonded to said repeating units. The hydrocarbon-containinggroups R₃ and R₄ that are contained may be two or more, respectively.

The above described modification may be carried out in the followingthree ways:

(I) R₃ (R₄) is substituted for the atom contained in AB or BA group inthe linear repeating units of formulae (1) to (3).

(II) R₃ (R₄) is substituted directly in R₁, R₂.

(III) R₃ (R₄) is substituted through the substituent of R₁, R₂ that isother than the group used in forming the linear repeating units of R₁,R₂.

Needless to say, (I), (II), and (III) may be used in combination, andR₃, R₄ may be the same or different.

To illustrate (I), (II), and (III) in more detail,

    ______________________________________                                        AB               BA                                                           ______________________________________                                         ##STR2##                                                                                       ##STR3##                                                     ##STR4##                                                                                       ##STR5##                                                     ##STR6##                                                                                       ##STR7##                                                    ______________________________________                                         R.sub.4 may be used in place of R.sub.3                                  

(I) is, as shown by the above table, a method wherein R₃ (R₄) issubstituted for the hydrogen atom on the nitrogen atom of AB or BA.

(II) is a method wherein R₃ (R₄) is substituted directly in R₁, R₂. Someof the examples are shown below. ##STR8##

(III) is a method which contains many possibilities as shown below inmore detail.

In the method of (III) at least one of R₁ and R₂ is at least trivalent,and R₃ (R₄) is substituted through the substituent which is other thanthe group used in forming the repeating units containing R₁, R₂. Ofcourse, though not limited to these, the following illustrate the caseswhere the valence cf R₁ is the same as or larger than that of R₂ withthe valence being taken to be up to 6.

    ______________________________________                                                 Valence of R.sub.1                                                                      Valance of R.sub.2                                         ______________________________________                                         ○1 3           2                                                       ○2 4           2                                                       ○3 5           2                                                       ○4 6           2                                                       ○5 3           3                                                       ○6 4           3                                                       ○7 5           3                                                       ○8 6           3                                                       ○9 4           4                                                       ○10                                                                              5           4                                                       ○11                                                                              6           4                                                       ○12                                                                              5           5                                                       ○13                                                                              6           5                                                       ○14                                                                              6           6                                                      ______________________________________                                    

Herein there are also listed up the examples in which R₁, R₂ are higherthan quintavalent, but R₁, R₂ are preferably up to tetravalent asfollows.

R₁ =3, R₂ =2 valent

R₁ =4, R₂ 2

R₁ =3, R₂ 3

R₁ =4, R₂ 3

R₁ =4, R₂ 4.

The possible examples are listed in the following.

When R₁ =3, R₂ =2, ##STR9##

In formulae (4) to (75) there are A/B which are not used in forming thelinear repeating units but (III) is the method by which R₃ (R₄) issubstituted through these substituent groups. For instance, if such agroup is A in (4) to (75), --COOR₃ (R₄), --CONHR₃ (R₄), --NHCOOR₃ (R₄),--NHCSOR₃ (R₄), --S02NHR₃ (R₄), etc., and if B, --NHR₃ (R₄), --OR₃ (R₄),--SR₃ (R₄), etc. can be substituted.

R₁, R₂ are an organic group which is at least divalent having at leasttwo carbon atoms, but they are preferably of the benzenoid unsaturationhaving at least 6 carbon atoms.

The term "benzenoid unsaturation" as used in this invention is used forthe structure of carbocyclic compounds in contrast to the quinoidstructure, and means the same structure as the carbon ring contained inthe ordinary aromatic compounds. ##STR10##

To explain R₁, R₂ in more detail, the preferable examples will be givenbelow. ##STR11## wherein R₅ is ##STR12## R₆ : alkyl or aryl group##STR13## and the like. ##STR14## (R₅ is as defined before) ##STR15##(R₅ is as defined before) ##STR16##

Of the foregoing more preferable examples for R₁ and R₂ are: ##STR17##(R₅ is as defined before)

R₃, R₄ are the hydrocarbon-containing groups of 10 to 30, preferably 16to 22 carbon atoms, and the preferable example is a monovalent groupselected from aliphatic group, aliphatic group bonded with alicyclicgroup, aliphatic group bonded with aromatic group, or the substituentgroup thereof as listed below. ##STR18##

Herein l+m=n-5, n=10-30, or preferably 16-22, and more preferableexamples are straight chain aliphatic hydrocarbon groups.

As the substituent groups there may be mentioned halogen atom, nitrogroup, amino group, cyano group, methoxy group, acetoxy group, etc., butthese are not indispensable, although fluorine atom is sometimes used inpreference because it can improve the hydrophobic property more thanhydrogen atom.

That is to say, the length of the alkyl chain can be shortened byintroduction of fluorine. For instance, in C₈ F₁₇ (CH₂)_(k) --, K=2 willsuffice, and film formation may be rendered possible with 10 carbonatom.

The actual examples of the high polymers which can be used in theprocess for forming a film of this invention will become clear bysubstituting in formulae (1) to (75) the actual examples of R₁, R₂, R₃,R₄, A, B, AB, and BA and the actual examples of the methods ofsubstituting R₃, R₄. Although no copolymer is contained in formulae (1)to (75), needless to say, the copolymers that can be known by analogyfrom them are also within the scope of this invention. The mixture ofthe high polymers in this invention are also within the scope of thisinvention.

Further, though not indispensable, the high polymers of this inventionmay be those which have been substituted by a group containing ahydrocarbon of 1 to 9 carbon atoms according to the method (I), (II), or(III).

The molecular weight of the high polymers of this invention is notparticularly limitative, and even when the molecular weight is low, filmformation is possible by the process of this invention, but the heatresistance, mechanical strength and chemical resistance of the filmobtained are not good. On the other hand, when the molecular weight istoo large, the viscosity also becomes too high for the film formation tobe feasible.

Accordingly, the number average molecular weight should preferably be onthe order of 2,000 to 300,000.

The practical examples of the high polymers of this invention which canbe derived from formulae (1) to (75) are as follows. ##STR19##

In the above formulae "→" indicates isomerization. For instance, thecase of formula (78) may be explained as follows. ##STR20##

This invention involves both cases where each of (78-1) and (78-2)exists singly and where (78-1) and (78-2) co-exist.

The other examples may be found in books such as "Heat Resistance ofHigh Polymer" (published by Baifukan, Mar. 5, 1970) and "ThermalDecomposition and Heat Resistance of High Polymer" (published byBaifukan, Mar. 15, 1974) edited by Hirotaro Kambe; etc.

Now with reference to the case where R₃ =R₄ =CH₃ (CH₂)₁₇ -- in formula(80) the process for preparation of these modified high polymers will beexplained below. The compound ##STR21## which is obtained by thealcoholysis of pyromellitic acid dianhydride is acylated with thionylchloride at a temperature of not lower than -10° C., a temperature up tonear the boiling point of the acid halide being preferable about 0°-40°C. in an organic polar solvent under a substantially anhydrouscondition, followed by reacting the resulting product withdiaminodiphenyl ether at a temperature of not lower than -10° C.,preferably -10° C. to +20° C., more preferably from 0° to +10° C.However, in the latter stage of the reaction, the use of reactiontemperature over 20° C. is favorable to complete the reaction. Theacylation and the amidation are usually carried out at a temperaturebetween about 0° C. to -10° C., but as the substituent groups such aslong chain alkyl groups, etc. have the tendency of freeze solidifying inthis invention, they should preferably be carried out at a temperatureof not lower than -10 ° C. In the above case, of course, either rawmaterials having different substituent groups may also be mixed to givecopolymers, or tetracarboxylic acid dianhydride or diamine having nosubstituent group or having substituent groups not more than 10 carbonatoms may be mixed in an amount of about 0 to 30%.

The amphiphilic polyimide precursor thus prepared may be used as thematerial of the LB film after having been separated and purified, or maybe made directly into a spreading solution of the LB film by addingchloroform, benzene, or the like thereto after the preparation.

Next, explanation will be given of the LB film used in this invention.

The process for forming LB film comprises spreading a film-formingmaterial on the surface of water, compressing the material thus spreadedon the surface of water at a constant surface pressure to form amonomolecular film, and then transferring the film formed onto asubstrate by repeatedly passing the substrate through the film. Besidesthe above described process (the vertical dipping method) there may bementioned horizontal dipping method, revolving cylindrical method, etc."Shin Jikken Kagaku Koza" vol. 18, "Interface and Colloid", 498-508).Thus, any of the processes usually carried out can be used optionally.

The Langmuir-Blodgett technique is an excellent method for formingoriented thin films of not less than 1000 Å, or of several hundreds Å orseveral tens Å in thickness with an accuracy of some tens Å, and thus,the thin films on the substrate of this invention may also have the samecharacteristics. However, even the films having a thickness of 10,000 Åor more can also be obtained by the technique.

In general, the solvent is selected from benzene, chloroform, etc. thatare insoluble in water and vaporise in the gaseous phase, but in thecase of the high polymers of this invention, it is desirable that inorder to enhance the solubility an organic polar solvent is used incombination. The preferable organic polar solvent isN,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide,N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, dimethyl sulfoxide,N-methyl-2-pyrrolidone, pyridine, dimethylsulfone,hexamethylphosphoramide,tetramethylenesulfone,dimethyltetramethylenesulfone, etc.

When benzene, chloroform, etc. are used in combination with the organicpolar solvent, it is considered that during the spreading benzene,chloroform, etc. vaporise into the gaseous phase, while the organicpolar solvent is dissolved in a large amount of water.

The substrate used in this invention is limited depending on to what thethin film of this invention is applicable, but otherwise there is noparticular limitation, so that as the substrate use can be made of notonly the general inorganic substrates such as glass, alumina, quartz,etc., but also metals, plastics, semiconductors of Groups IV, III-V,II-VI, etc. such as Si, GaAs, ZnS; ferroelectric substances such asPbTiO₃, BaTiO₃, LiNbO₃, LiTaO₃ ; etc. Also, use can of course be made ofthose which were subjected to surface treatment as usually carried outin practice.

This invention is characterized in that high polymers having a good heatresistance can be formed into thin films on a substrate by theLangmuir-Blodgett technique, and moreover, in some cases thin filmshaving a still further improved heat resistance can be formed on asubstrate by causing ring closure to take place partially or wholly inthe thin films.

Among the examples of (76) to (95), (78) to (90) are the cases where thering closure takes place partially or wholly to form a five- orsix-membered ring containing hetero atoms, with the structure after thecomplete ring closure being shown below. ##STR22##

There is no particular limitation to the process for ring closure, but,for instance, in the case of the imidation of the isomeric compound ofthe formula (80), by heating to 200° to 400° C., the following reactiontakes place and the ring closure is accomplished.

High polymer of formula (80) ##STR23##

In the above case, the group which was introduced for the purpose ofincreasing the hydrophobicity is eliminated as an alcohol, but as theeliminated alcohol can be removed at a temperatures of 200° to 400° C.,if required, under a gas flow or a vacuum, highly heat-resistantpolyimide thin films can be obtained.

Now, reference will be made to the uses of these thin films.

The thin films of this invention can be used not only in the field ofelectronics, but also in the extensive fields such as energy conversion,material separation, etc. by making the most of the characteristicfeature such that they are extremely thin films excellent in heatresistance, chemical resistance, and mechanical strength.

In the field of electronics, wherein conductivity, photo-conductivity,optical characteristics, insulating ability, thermal characteristics, orchemical reactivity are made the most of, they can be used as opticalrecording film, resist film, insulating film, thin film for capacitor,liquid crystal orientation film, polarizing film, sensor film, etc., andabove all, as the insulating film, they can be used as the insulatinglayer in the electrical and electronic elements having the structure ofMIS, MIM, etc. in which various kinds of semiconductors or metals havebeen combined therewith as the insulating layer of IC or LSI, and also,can be made into field-effect transistor, photoelectric device, lightemitting device, light receiving device, light detecting device,thermionic transistor, etc. In particular, the thin films of thisinvention are effective in MIS, MIM devices utilizing tunnel effect, andalso, can be used as the insulating film of JJ (Josephson Junction).

Besides the above it is considered that the thin films of this inventioncan also be used as the cladding material or the optical circuit elementfor waveguide.

In all the fields they will also be adapted for use as coating materialfor protection, and further, in the techniques generally used in thefield of the LB film to obtain the mixed film or laminated film of thefunctional LB material and fatty acid, if the high polymer of thisinvention is used in place of the fatty acid, it is possible to obtainfilms which can manifest various functions, so that many uses areconsidered for these films. For instance, by preparing the filmscontaining dyes, enzymes, etc. photoelectric sensing element, biosensor,etc. can be obtained.

Still further, the use of these films in the field of materialseparation may also be considered.

With reference to some examples the process for preparation of the highpolymers of this invention and the process for forming films will beexplained below.

EXAMPLE 1

2.18 g (0.01 mole) of pyrromellitic acid dianhydride and 5.40 g (0.02mole) of stearyl alcohol were reacted at about 100° C. for 3 hours in aflask while passing dry nitrogen therethrough.

The reaction product obtained was dissolved in 40 cc ofhexamethylphosphoramide and cooled to 0° to 5° C. Then 2.38 g ofthionylchloride was dropwise added thereto at about 5° C., and after thedropping about 5° C. was maintained for one hour and the reaction wascompleted.

Thereafter 2 g (0.01 mole) of diaminodiphenyl ether dissolved in 50 ccof dimethylacetamide was dropwise added at 0° to 5° C., and after thedropping the reaction was continued for about one hour, and then thereaction mixture was poured into 600 cc of distilled water toprecipitate the reaction product, which was filtered and dried at 40° C.to give about 9 g of pale yellow powder.

IR spectrum analysis, thermogravimetric analysis (TGA-DTA), andmeasurement of molecular weight by GPC were carried out with thefollowing results.

IR Spectrum Analysis

The IR chart taken by KBr disc process is as shown in FIG. 1, in whichthe characteristic absorptions of ester, amide I, II, III, alkyl chain,and ether are seen.

Thermal Analysis (TGA-DTA)

The result of the measurement using an apparatus of RTG-DTA (H) typeanalyser manufactured by Rigaku Denki with full scale 10 mg for TGA and100 μV for DTA by elevating the temperature at a rate of 10° C./min to1000° C., in a nitrogen flow (30 ml/min) is as shown in FIG. 2. In theTGA there are inflection points at 192°, 271°, 318°, 396° and 592° C.,and in the DTA there is a characteristic peak near 657° C.

On the other hand FIG. 3 shows the result when the temperature wasraised to 400° C. at a rate of 10° C./min. and after having been held at400° C. for one hour, returned to room temperature, and then raised to1000° C. at a rate of 10° C./min. By holding the temperature at 400° C.for one hour the weight attained almost a constant weight indicating thetermination of the polyimidation reaction. Even when this product wascooled to room temperature and again heated there was no change in theweight until exceeding 450° C., and it was clearly shown that thethermal decomposition begins at 584° C. which is just the same as thethermal decomposition temperature of polyimide film. Thus, it was foundthat by the termination of the polyimidation reaction there is obtaineda product whose heat resistance is comparable to that of polyimide film.

Measurement of Molecular Weight by GPC

The number average molecular weight which was computed by comparing theresult of GPC measured in N,N-dimethylacetamide solvent with thestandard sample of polystyrene was about 50,000.

EXAMPLE 2

25 ml of developing solution for LB film was prepared by dissolving 55.1mg of the product in Example 1 in a mixed liquid of distilledchloroform/dimethylacetamide=8/2 (volume ratio).

On the surface of bi-distilled water at 20° C. the relation between thesurface pressure and the area per repeating unit was measured, and therewas obtained the result as shown in FIG. 4. The surface pressure risesrapidly from about 75 Å² /unit and a good condensed film was formed. Thelimiting area was 60 Å² /unit and the collapse pressure was also foundto be 55 dyne/cm which is an extremely high value as high polymer film.Further, even when the film was held on the surface of water maintainingthe surface pressure at 25 dyne/cm no decrease in the area wasrecognized over two hours, indicating the stability of the film.

Next, maintaining the surface pressure of the film on the surface ofwater at 25 dyne/cm, built-up films of 61 and 60 layers, respectively,were deposited on a glass substrate and a CaF₂ plate at a dipping speedof 10 mm/min by LB technique. From the film obtained on the CaF₂ platethere was obtained FT-IR spectrum as shown in FIG. 5, which was found tocoincide with IR of the compound obtained in Example 1. It was alsoconfirmed that the built-up film was a Y type film according to thearea-time curve. Further, in the X-ray diffraction of the built-up film,one peak was observed at 2θ=4.65° despite that no Cd⁺⁺ ion was includedin water used in this example.

Also, the built-up film obtained was about 1800 Å in thickness, andfound to have a good insulation characteristic from the measurement ofthe capacitance.

Further, it was also confirmed from the peaks at 1790 and 1710 cm⁻¹ byFT-IR analysis that by heating the built-up film at 400° C. for one hourthere is formed α, β-unsaturated five-membered ring imide.

On the other hand, it has been confirmed from the IR spectrum that whenthe product in Example 1 is heated at 400° C. for one hour imidationreaction takes place resulting in a decrease of 58 wt % in the weight,which is in precisely conformity with the calculated value, 58.7%, whenit is assumed that stearyl alcohol is eliminated by the imidation.

EXAMPLE 3

A polyimide precursor was synthesized in the same manner as Example 1except that n-decyl alcohol (n--C₁₀ H₂₁ OH) was used in place of stearylalcohol. The polyimide precursor showed the same characteristics asthose of the polyimide in Example 1 by IR spectrum analysis, thermalanalysis, and measurement of molecular weight by GPC, but the result ofthe measurement of the surface pressure vs. area curve is as shown inFIG. 6, in which there is found only the liquid expansion phase, but notthe condensation phase. This clearly indicates that the alkyl grouphaving 10 carbon atoms is too short in the chain length to obtain astable monomolecular layer. For instance, the film maintained at 20dyne/cm in surface pressure on the water surface was unstable, thus theprecursor obtained in this Example did not give a good built-up film.

EXAMPLE 4

Polyimide precursors were prepared in the same manner as in Example 1except that lauryl alcohol (C₁₂), myristyl alcohol (C₁₄) or cetylalcohol (C₁₆) was used instead of stearyl alcohol.

The obtained precursor by using the C₁₂ or C₁₄ alcohol showed behaviorsintermediate between those for C₁₀ and C₁₈, and formed a sufficientlystable monolayer and could form a built-up film.

The precursor obtained by using the C₁₆ alcohol formed a very stablemonolayer on the water surface and could form a good built-up film.

Also, it was confirmed that the precursors obtained in these Exampleswere converted into polyimides by heat treatment.

EXAMPLE 5

Using trimellitic acid anhydride (0.01 mole) and stearyl alcohol (0.01mole) in the same manner as in Example 1, monostearyl trimellitic acidester was synthesized, and after acylating with thionyl chloride,diaminodiphenyl ether (0.01 mole) was reacted to give 2.12 g of whitepowder.

FIGS. 7 and 8 are the results of IR spectrum analysis andthermogravimetric analysis (TGA-DTA) of the product.

The IR spectrum analysis indicated the characteristic absorption thesame in Example 1. Also, by the thermal analysis there are seendistinguished inflection points at 207° and 262° C. in TGA, and it wasconfirmed by the IR spectrum that after the inflection point at 262° C.,the imidation is complete and polyamideimide is formed.

EXAMPLE 6

In the same manner as in Example 2, the relation between the surfacepressure and the area per repeating unit was measured, with the resultbeing shown in FIG. 9.

The collapse pressure was as high as 45 dyne/cm, and a good condensedfilm could be formed. The limiting area was 60 Å² /unit.

Further it was also confirmed that by maintaining the surface pressureat 25 dyne/cm the film of Y type can be built up on a glass substrate ata dipping speed of 10 mm/min. by LB technique.

According the present invention, there is to made feasible the filmformation by the Langmuir-Blodgett technique, by modifying the highpolymers which are inherently difficult to be formed into film accordingto the LB technique, and to provide high polymer films which have athickness hitherto never obtained easily such as in 10,000 Å, ifrequired 10-1000 Å, by partially or completely cyclizing the componentthereof, and which exhibit improved heat resistance, chemical resistanceand mechanical characteristics.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A built-up film formed by a Langmuir-Blodgetttechnique from a polymer which consists essentially of:(i) a skeleton oflinear repeating units, wherein each of said linear repeating units arecomposed of a first organic group R₁ and a second organic group R₂, eachof R₁ and R₂ being at least divalent and having at least two carbonatoms, R₁ and R₂ being connected with each other by a divalent bondinggroup formed by reaction of an acidic group containing a heteroatom anda basic group containing a heteroatom, and (ii) at least one groupselected from hydrocarbon-containing groups R₃ and R₄ and bonded to thelinear repeating units by covalent bonding, wherein each of R₃ and R₄ isindependently a hydrocarbon-containing group of 10 to 30 carbon atomswhich may contain substituent groups, with the proviso that when any oneof the groups selected from R₃ and R₄ has 10 or 11 carbon atoms, thensaid group selected from R₃ and R₄ and having 10 or 11 carbon atoms mustcontain fluorine as said substituent groups.
 2. A built-up filmaccording to claim 1, wherein the average molecular weight of saidpolymer is in the range of 2,000 to 300,000.
 3. A built-up filmaccording to claim 1, wherein at least one of the groups R₁ and R₂ is abenzenoid group having at least 6 carbon atoms.
 4. A built-up filmaccording to claim 1, wherein both of the groups R₃ and R₄ are bonded tothe same repeating unit.
 5. A built-up film according to claim 1,wherein each of the groups R₃ and R₄ has 16 to 22 carbon atoms.